Introduction

Slip resistance of floors and pavements is a measure of the ability of a surface to resist accidental slipping by pedestrians - in dry or wet conditions. There is an expectation that surfaces will provide adequate slip resistance and this is increasingly being incorporated into regulations.

Polished concrete floors is a generic term that describes a variety of exposed decorative concrete flooring options often having a highly polished or gloss surface finish. With the increasing popularity of these types of finishes the issue of providing adequate slip resistance has become an important consideration.

This data sheet examines the factors influencing the slip resistance of a surface and methods of measuring, specifying, achieving, maintaining and improving slip resistance. It focuses on the factors related to the concrete floor or pavement surface that impact on the risk of slipping, which include the surface finish, texture and applied sealer (if present) that combine to produce a final surface roughness. A number of case studies have been examined to determine the factors contributing to whether or not the specified slip resistance was achieved.

"Slip resistance of floors and pavements is a measure of the ability of a surface to resist accidental slipping by pedestrians - in dry or wet conditions"

Factors Influencing Slip Resistance

Pedestrian slip resistance is a complex subject, where the likelihood of a slip is a function of a variety of factors such as the surface (type and texture), the environmental conditions, and the individual users (their physical condition and footwear). The reasons for accidental falls on concrete surfaces can be divided into four categories:

External factors - These are essentially hazards such as stepping (vertical displacement) at footpath cracks and other slab joints, slippery floor surfaces and slopes. These can be minimised through good design and installation practices, good cleaning and maintenance practices safety audits, remedial policies, and mandatory legislation. Footwear may be considered an external factor, since inappropriate or excessively worn footwear may be the primary cause of an accident.

Internal factors - These include voluntary and involuntary responses of people to environmental factors such as distractions. Responses may also be influenced by stress, fatigue, medicinal and recreational drugs, and also by the person's mood and the degree of preoccupation (which may be influenced by the nature of the activity being undertaken - carrying, pushing, rushing), and whether it imposes a temporary functional limitation, e.g. obscured vision or impaired balance.

Environmental factors - These include lighting conditions, contamination of the surface (by water or other materials) and slopes. The risks can be minimised by good design practices (lower gradients, less glare) and staff training (response to spills, replacement of light bulbs).

Sufficient micro-roughness is necessary to provide the fictional force or 'grip' required to prevent footwear (and bare feet) from slipping. Micro-roughness is the irregularities in a walking surface, often invisible to the naked eye, with a surface roughness (Rz) typically between 10μm and 100μm as measured by a surface roughness meter. The coarser the surface roughness, the greater will be the slip resistance, especially when contaminated by water or a range of other substances. This is dealt with in more detail in the section on improving slip resistance.

Measuring Slip Resistance

While the surface roughness can be measured, the two common methods used to assess wet slip resistance are the wet pendulum test, which measures the frictional force offered by simulating a foot moving over a water-contaminated surface, and the ramp test, which determines the maximum gradient at which a person can just traverse the surface, either barefoot (wet barefoot test) or in shoes (oil-wet test). AS/NZS 45863 also includes a friction test method for dry floors. Since most wet floors will provide adequate slip resistance when clean and dry, this test is not commonly specified.

Wet Pendulum Test - This test (AS/NZS 4586) is generally used in the laboratory for classifying the wet slip resistance of new flooring (pedestrian surface) materials. However, as the test instrument is portable Figure 1, it can also be used on site to assess the slip resistance of existing floors and pavements (AS/NZS 46634).

The instrument has a rubber slider attached to a spring-loaded foot at the end of a pendulum arm (leg). The pendulum arm is released from a horizontal position, allowing it to swing so that the slider contacts the wet pedestrian surface over a set distance of 126mm. The extent to which the pendulum fails to read its release height on the oversewing is used as a measurement of the slip resistance. The reading on the scale is the British Pendulum Number (BPN).

The AS/NZS 4568 classifications for slip resistance based on this test using a Four S (simulated standard shoe sole) rubber are given in Table 1. Note that a TRL (Transport Research Laboratory) rubber can also be used (listed in Table 2 of AS/NZS 4586) but the results are sensitive to temperature and a correction must be applied. A Four S rubber is typically specified as it is generally considered to best differentiate between the slip resistance of smoother surfaces. The TRL rubber is sometimes used when considering wet barefoot slip resistance. Figure 1

Ramp Tests - These tests use human subjects to subjectively assess the slip resistance of pedestrian surfaces under closely controlled conditions. The subjects walk forwards and backwards on a ramp (Figure 2) while the operator progressively increases the angle of inclination, until the subjects reach the 'zone of insecurity' where they either experience slipping or sense that they will fall if the angle is further increased. The angles of inclination reached are used to assess the friction characteristics of the test surface. The test is not intended to provide guidance on the angle of ramps for which a particular classification is suitable. There are two principal test methods: the wet barefoot test and the oil-wet test.

Wet Barefoot Test - For the test procedure described above, the subjects are barefoot and water is applied to the surface being tested. This method is accepted as the best means for assessing the slip resistance of materials that are intended for use in barefoot areas, such as showers and swimming pools.

Oil-Wet Test - This involves coating the material surface with engine lubricating oil, and having two test subjects wearing standard test shoes, walking forwards and backwards on the ramp to determine the inclination at which safe walking is no longer possible. Facing downhill and with an upright posture, each subject in turn moves backwards and forwards over the test surface as the angle of inclination is gradually increased, until the safe limit of walking is reached. Subjective influences on the acceptance are limited by means of calibration procedure. This test method is accepted as best means for assessing the slip resistance of materials that are intended for use in industrial premises, where the nature and extent of the contamination can be predicted, and staff can be compelled to wear appropriate footwear.